With engine off, clicking noise under hood at.

Quite a few possibilities exist for the noise. Start withthe cover over the shaft if it has one, some of these can become dislodged and touch the steering coupler loint making noise, the coupler itself could have loose fasteners of bad insulator, the steering box itself may make noise if internal parts have excessive play, then there is the linkage such as tie rods. Any reputable fornt end shop should be able to test all of those. If you want to tackle it yourself my best suggestion is to get a piece of garden hose approx 3 ft long, hold one end to your ear and while having an assistant turn the wheel back and forth, move the free end of the hose around and see where the noise is loudest. Good Luck.